1. Field of the Invention
The present invention relates to a nutating step motor for producing the rotation of the output shaft thereof with a high torque and a low speed caused by the difference in the number of teeth between a crown gear on a wobble disc of magnetic body which wobbles as it is successively attracted by each of annularly arranged electromagnets when it is energized successively, and another crown gear fixedly arranged on the magnetically permeable cores of the electromagnets.
The step motor according to the present invention is not only optimum for machine tools which require a low speed revolution under a computer numerical control, mainly such as various industrial robots, business machines, NC, MC, etc., but also has features useful in various fields such that it can be directly coupled to a machine tool which requires a very low speed revolution without using a reduction gear.
2. Description of the Related Art
A conventional step motor of this kind s disclosed in U.S. Pat. No. 3,644,764 which expired Feb. 22, 1989 as illustrated in FIG. 1 of the attached drawings. The motor a attracts a wobble disc b of magnetic body by the electromagnetic force of an energized electromagnet e thereby to produce mating contact between a crown gear c provided at the outer circumferential portion b.sub.2 of the wobble disc b and a crown gear d which is provided on the side of the frame in such a way as to confront the crown gear c, so that the wobble disc b continues wobbling.
At that time, the wobble disc b only wobbles circularly by magnetic attractive force but does not rotate at all. An inner crown gear f provided on the wobble disc b adjacent to the center thereof mates with a crown gear h provided at the end portion i of the output shaft g in such a way as to confront the inner crown gear f as a result of the wobbling of the wobble disc b, so that the output shaft g, is rotated due to the difference in the number of teeth between the inner crown gear f and the crown gear h.
Accordingly, the output shaft turns due to the difference in the number of teeth between the inner crown gear f and the crown gear h, i.e., which is usually one or two, as a result of a cycle of wobbling of the wobble disc b.
(1) As illustrated in FIG. 1, the step motor wobbles smoothly by the crown gear c provided at the outer circumferential portion b.sub.2 of the wobble disc b and the crown gear d which is provided on the side of the frame so as to confront the crown gear c. The step motor is further provided with a crown gear f on the wobble disc 1 inside the crown gear c and a crown gear h on the output shaft for rotating the same.
Since the step motor is provided with two sets of gears, i.e., the crown gears c and d which mate with each other as a result of wobbling of the wobble disc b and the crown gears f and h for rotating the output shaft thereof, it is complicated in structure and costs high.
(2) The inner crown gears f and h for rotating the output shaft thereof due to the difference in the number of teeth therebetween illustrated in FIG. 1 are small in pitch circle diameters and inevitably cannot have many teeth in order to obtain a high torque at a low speed since they are provided inside and the pitch of the teeth is determined as illustrated in FIG. 2, so that the step motor cannot prove the merit of the low speed motor.
(3) Moreover, when the inner crown gears f and h for rotating the output shaft cannot have many teeth, it is not only difficult to position the step angle with accuracy but also there occur problems that the teeth wear out rapidly to cause damages, the lives of the devices are shortened, and so on.
(4) Since the step motor has to be provided with the crown gears c and d for only mating with each other by the wobbling of the wobble disc b and the crown gears f and h for rotating the output shaft, it need many gears, so that it is complicated in structure, troublesome in assembling and expensive in manufacturing.
It is the object of the present invention to solve the problems (1) thru (4) set forth above.